The MurG glycosyltransferase provides an oligomeric scaffold for the cytoplasmic steps of peptidoglycan biosynthesis in the human pathogen Bordetella pertussis

Peptidoglycan is a major component of the bacterial cell wall and thus a major determinant of cell shape. Its biosynthesis is initiated by several sequential reactions catalyzed by cytoplasmic Mur enzymes. Mur ligases (MurC, -D, -E, and -F) are essential for bacteria, metabolize molecules not present in eukaryotes, and are structurally and biochemically tractable. However, although many Mur inhibitors have been developed, few have shown promising antibacterial activity, prompting the hypothesis that within the cytoplasm, Mur enzymes could exist as a complex whose architecture limits access of small molecules to their active sites. This suggestion is supported by the observation that in many bacteria, mur genes are present in a single operon, and pairs of these genes often are fused to generate a single polypeptide. Here, we explored this genetic arrangement in the human pathogen Bordetella pertussis and show that MurE and MurF are expressed as a single, bifunctional protein. EM, small angle X-ray scattering (SAXS), and analytical centrifugation (AUC) revealed that the MurE-MurF fusion displays an elongated, flexible structure that can dimerize. Moreover, MurE-MurF interacted with the peripheral glycosyltransferase MurG, which formed discrete oligomers resembling 4- or 5-armed stars in EM images. The oligomeric structure of MurG may allow it to play a bona fide scaffolding role for a potential Mur complex, facilitating the efficient conveyance of peptidoglycan-building blocks toward the inner membrane leaflet. Our findings shed light on the structural determinants of a peptidoglycan formation complex involving Mur enzymes in bacterial cell wall formation9FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP11/52067-6; 2017/12436-9; 2013/02451-0FRISBI [ANR-10-INSB-05-02]; GRAL within the Grenoble Partnership for Structural Biology (PSB) [ANR-10-LABX-49-01]; Rhone-Alpes RegionRegion Auvergne-Rhone-Alpes; Fondation pour la Recherche Medicale (FRM)Fondation pour la Recherche Medicale; fonds FEDER; Centre National de la Recherche Scientifique (CNRS)Centre National de la Recherche Scientifique (CNRS); Commissariat a l'Energie Atomique et aux Energies Alternatives (CEA)French Atomic Energy Commission; University of Grenoble Alpes; EMBL; GIS-Infrastructures en Biologie Sante et Agronomie (IBISA); Laboratoire International Associe BACWALL (CNRS); FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [11/52067-6, 2017/12436-9]; Agence Nationale de la RechercheFrench National Research Agency (ANR) [ANR-13-BSV8-0015-01]; ANRFrench National Research Agency (ANR); Fondation pour la Recherche Medicale (FRM)Fondation pour la Recherche Medicale [FDT20160435484]; FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2013/02451-0

DET1-mediated degradation of a SAGA-like deubiquitination module controls H2Bub homeostasis

DE-ETIOLATED 1 (DET1) is an evolutionarily conserved component of the ubiquitination machinery that mediates the destabilization of key regulators of cell differentiation and proliferation in multicellular organisms. In this study, we provide evidence from Arabidopsis that DET1 is essential for the regulation of histone H2B monoubiquitination (H2Bub) over most genes by controlling the stability of a deubiquitination module (DUBm). In contrast with yeast and metazoan DUB modules that are associated with the large SAGA complex, the Arabidopsis DUBm only comprises three proteins (hereafter named SGF11, ENY2 and UBP22) and appears to act independently as a major H2Bub deubiquitinase activity. Our study further unveils that DET1-DDB1-Associated-1 (DDA1) protein interacts with SGF11 in vivo, linking the DET1 complex to light-dependent ubiquitin-mediated proteolytic degradation of the DUBm. Collectively, these findings uncover a signaling path controlling DUBm availability, potentially adjusting H2Bub turnover capacity to the cell transcriptional status